The present invention relates to a process for in-situ biodegradation of hydrocarbon contaminated soil, and for containment of the contaminated groundwater to prevent the spread of the contamination. More specifically the invention is an apparatus and process for containing and/or treating groundwater contaminated by an organic compound, such as a petroleum product and for biodegrading in-situ such organic compound, which is contaminating a particulate solid, such as soil.
Under present technologies, ground and groundwater, which are determined to be contaminated by organic compounds such as a petroleum product, are treated through the use of air stripping towers and groundwater withdrawal systems. Generally, a well is drilled into the ground to a depth equal to the vertical extent of contamination. A pump is installed and groundwater is withdrawn from the well and pumped to an above ground air-stripping tower. Pressurized air is pumped into the tower from the bottom and comes into contact with the contaminated water travelling down the tower. The contaminants attach themselves to the air molecules (a function of vapor pressure) and are carried upward into the atmosphere. Treated groundwater is discharged back into the ground for subsequent withdrawal and retreatment or are disposed of off-site. There are two basic disadvantages of air stripping technology.
First, only excessively contaminated soils are typically removed, and residual contamination from the soil can continue to recontaminate the groundwater and prolong air stripping requirements as well as regulatory approvals and delays. Air stripping is only as effective as the ability of the particular soil to release water (and contaminants) from the soil pore spaces, as a result, loose sands can be cleaned with air stripping fairly well, but clays or other loamy sands are not well suited for the air stripping process.
Second, air stripping releases pollutants to the atmosphere, and the pollutant is merely being moved from the water we drink to the air we breathe. Current regulations on air pollution are strengthening due to public pressure. The most obvious air pollutant is smog. When volatiles are released at ground level, sunlight generates photochemical reactions with volatiles and the releases contribute to the formation of smog. Air stripping will require charcoal filtration and liquid recovery in the future as is presently required in California increasing the expense of this technique.
Typical in-situ bioremediation systems, as presently practiced, introduce organisms and/or stimulate indigenous bacteria. This technique can take up to several months depending on the hydrogeological setting. Some of the problems encountered with such bioremediation include following: keeping the bacteria alive until the pollutants reach them, or until they reach the hydrocarbon pollutant which is the food source; the difficulty of controlling oxygen content, nutrient levels and temperature in the field. All three variables are easy to control in the laboratory or in above ground systems, but are difficult to control underground in the field; and monitoring the bacteria degradation rates often becomes difficult. When excess bacteria are introduced, the bacteria become anaerobic and generate methane gas as a waste product. Methane is a combustible gas and large build ups from failed bioremediation attempts have impeded regulatory acceptance to bioremediation.
Bioremediation and biodegradation have been proposed for remediation of hydrocarbon contamination. See, for example, the following U.S. Pat. Nos.: Linn, 3,616,204; Ely et al., 4,765,902; Raymond, 3,846,290; Thirumalachar et al., 4,415,661; Thirumalachar et al., 4,415,662; Lavigne, 4,678,582; Norris et al., 4,849,360; and Hater et al., 4,850,745.
Each of the above mentioned patents suffer from a failure to provide a fully integrated system for the confinement of and reclamation of a hydrocarbon contaminated site.